Hatpin Province is at a tropical zone in South China. Zooplankton diversity there has rarely been investigated. 1n orderto collect basic data and understand the community structure of rotifers in Hainan Province, seven typi;al reservoirs were sampledin December of 2006 and May of 2007. 32 species were identified, among which the majority was eurythermal or mesophilic spe-cies. In the two sampling periods, the dominant species and their relative dominance in abundance varied between different reser-voirs, almost all the dominant species were small sized ones with armor. The dominant species were Brachionus fofcula and Bra-chionus falcatus in the early flood season and Filinia cama.secla in the late dry season. The average abundance and biomass of roti-fers were 66. Bind/L and 21.6ug/L, respectively, which both were lower than those in the subtropics and temperate zones. Ingeneral, the rotifers were characterized by low species diversity, small body size and low abundance. Although the relative abun-dance of the dominant rotifers varied slightly between the dry and flood seasons, the consistent species composition indicates thatthe rotifers keep a steadily community structure in the tropical reservoirs.